Coronary artery disease remains the leading cause of morbidity and mortality in Western societies. Coronary artery disease is manifested in a number of ways. For example, disease of the coronary arteries can lead to insufficient blood flow to various areas of the heart. This can lead to the discomfort of angina and the risk of ischemia. In severe cases, acute blockage of coronary blood flow can result in irreversible damage to the myocardial tissue including myocardial infarction and the risk of death.
A number of approaches have been developed for treating coronary artery disease. In less severe cases, it is often sufficient to merely treat the symptoms, with pharmaceuticals, or treat the underlying causes of the disease, with lifestyle modification. In more severe cases, the coronary blockage can be treated endovascularly or percutaneously using techniques such as balloon angioplasty, atherectomy, laser ablation, stents, and the like.
In cases where these approaches have failed or are likely to fail, it is often necessary to perform a coronary artery bypass graft procedure. This procedure generally consists of the following steps: First, direct access to the heart is achieved. This is usually done by opening the chest by median sternotomy and spreading the left and right rib cage apart; and opening the pericardial sac to achieve direct access to the heart.
Next, a blood vessel or vessels for use in the graft procedure are mobilized from the patient. This usually entails mobilizing either a mammary artery or a saphenous vein, although other graft vessels may also be used.
Next, a heart-lung or cardiopulmonary bypass is performed. This usually entails arterial and venous cannulation, connecting the bloodstream to a heart-lung machine, cooling the body to about 32 degrees Celsius, cross-clamping of the aorta and cardioplegic perfusion of the coronary arteries to arrest and cool the heart to about 4 degrees Celsius. The arrest or stoppage of the heart is generally required because the constant pumping motion of the beating heart would make surgery upon the heart difficult in some locations and extremely difficult if not impossible in other locations
Once cardiac arrest is achieved, then a graft (or grafts) is attached to the relevant portions of a coronary artery (or arteries) followed by weaning from the cardiopulmonary bypass, restarting the heart and decannulation. Finally the chest is closed.
One area which may create difficulties for the patient and extra expense and time for the procedure involves the cardiopulmonary bypass. In a cardiopulmonary bypass all the patient's blood, which normally returns to the right atrium, is diverted to a system which supplies oxygen to the blood and removes carbon dioxide and returns the blood, at sufficient pressure, into the patient's aorta for further distribution into the body. Generally such a system requires several separate components, including an oxygenator, several pumps, a reservoir, a blood temperature control system, filters as well as flow, pressure and temperature sensors.
Problems may develop during cardiopulmonary bypass due to the reaction blood has to non-endothelially lined surfaces, i.e. surfaces unlike those of a blood vessel. In particular, exposure of blood to foreign surfaces results in the activation of virtually all the humoral and cellular components of the inflammatory response, as well as some of the slower reacting specific immune responses. Other complications from cardiopulmonary bypass include loss of red blood cells and platelets due to shear stress damage. In addition, cardiopulmonary bypass requires the use of an anticoagulant, such as heparin. This may, in turn, increase the risk of hemorrhage. Finally cardiopulmonary bypass sometimes necessitates giving additional blood to the patient. The additional blood, if from a source other than the patient, may expose the patient to blood born diseases.
Due to the risks incurred during cardiopulmonary bypass, others have attempted to perform a coronary artery bypass graft procedure without cardiac arrest and cardiopulmonary bypass. For example, Trapp and Bisarya in “Placement of Coronary Artery Bypass Graft Without Pump Oxygenator”, Annals Thorac. Surg. Vol. 19, No. 1, (January 1975) pgs. 1–9, immobilized the area of the bypass graft by encircling sutures deep enough to incorporate enough muscle to suspend an area of the heart and prevent damage to the coronary artery. More recently Fanning et al. in “Reoperative Coronary Artery Bypass Grafting Without Cardiopulmonary Bypass”, Annals Thorac. Surg. Vol. 55, (February 1993) pgs. 486–489 also reported immobilizing the area of the bypass graft with stabilization sutures.
Current beating heart bypass surgery techniques demand relatively motionless epicardial tissue in the immediate vicinity of an anastomosis. Several systems are presently available which attempt to immobilize epicardial tissue in the immediate vicinity of an anastomosis through a simple mechanical fork. One of the many such systems presently available includes the Access™ system available from CardioThoracic Systems Inc., Cupertino, Calif. Such a system stabilizes the heart by pressing a fork downwards onto the heart surface. Through this pressure the region of the epicardium between the fork is immobilized. Commercially available systems use short arms mounted to retractors in close proximity to the chest cavity. Mechanical fork systems only operate successfully on vessels that can be immobilized by applying pressure in a downward direction. These systems are very useful for operations on the anterior portion of the heart (such as the left anterior descending artery). However, fork systems are limited in their ability to maneuver a vessel into better view or for operating on the posterior portion of the heart. That is, fork systems are limited in their ability to “present” a vessel to the surgeon. This is a even greater drawback since fork systems stabilize only through compression, therefore often pushing downwards the are of surgical interest. In addition, compression of the heart can lead to diminished cardiac output, presenting a further risk to the patient's well-being. Finally, such systems, to date, have often featured rigid, inflexible arms which often interfere with the view or movements or both of the surgeon.
Suction stabilization systems, such as the Medtronic Octopus® Tissue Stabilizer and Accessories (available from Medtronic, Inc., Minneapolis, Minn. USA), use comparatively long, dual reusable articulating arms configured with clamps at their distal ends to secure suction based tissue stabilizers. During use, the arms are typically secured to a rail on the side of the operating table. The suction grips and immobilizes the surface of the heart. Additionally, the system allows the surgeon to manipulate the anastomosis site into better view by rotating and supporting the heart. The system also allows the surgeon to apply tension to the tissue between the stabilizers. Thus, the system is much more versatile than mechanical fork style systems. The suction paddles or pods can attach to and immobilize the heart, and can be used to manipulate the heart into better position so that the more difficult to reach vessels can be bypassed.
Many surgeons have used the Medtronic Octopus® Tissue Stabilizer system to perform as many as five or six vessel bypasses. Some surgeons, in fact, report using the product on 50–90% of their cases. Nonetheless such a system is still in need of improvement. For example, such a system was relatively more cumbersome to set up than desired, requiring each stabilization arm to be individually fixed or immobilized. Moreover, because each arm worked individually, spreading the arms relatively apart was more difficult than desired. Finally, because the degree of spreading was not limited in any way, surgeons could spread the paddles apart at greater distance than desired, causing one or both paddles to spontaneously lose capture of the tissue.
While these past products and attempts have achieved some success, their still exists a need to provide a method and apparatus for performing beating heart surgery which readily and quickly permits the immobilization or stabilization of a local area of tissue.
The present invention concerns an advanced system for immobilizing or stabilizing a local area of tissue.